Spun yarn and its doubled yarn and the process for manufacturing the same

ABSTRACT

A method for producing spun yarn in an open-end spinning system having a rotary open-ended spinning chamber comprises feeding a bundle of fibers to the open-ended spinning chamber, rotating the open-ended spinning chamber at a peripheral surface speed V to successively accumulate superimposed layers of fibers upon the peripheral surface of the spinning chamber, withdrawing the accumulated fiber layers from the rotating open-ended spinning chamber in the form of spun yarn at a withdrawing speed W to self-double the spun yarn at a doubling number V/W, and selectively varying the speeds V and W to provide the spun yarn with a predetermined doubling number V/W during only a single passage through the open-end spinning system. The bundle of fibers is fed to the spinning chamber in a compressed air stream which transports the fibers in a mutually liberated condition to the open-ended spinning chamber.

United States Patent Tabata et al.

[111 3,768,246 1 1 Oct. so, 1973 SPUN YARN AND ITS DOUBLED YARN AND THEPROCESS FOR MANUFACTURING THE SAME Inventors: Masaaki Tabata; KozoSusami;

IIiroshi Edagawa, all of Otsu-shi, Japan Assignee: Toray Industries,Inc.

Filed: Dec. 24, 1969 Appl. No.: 888,093

Related US. Application Data Division of Ser. No. 691,056, Dec. 15,1967, Pat. No. 3,501,907.

Foreign Application Priority Data Dec. 20, 1966 Japan 41/8298 July 12,1967 Japan 42/44377 us. C1. 57/156, 57/5889 Int. Cl D0111 1/12 Field ofSearch 57/5889, 58.91,

References Cited UNITED STATES PATENTS 1/1930 Gross 57/5893 UX 1/1965.luillard, 57/5889 3,399,523 9/1968 Ripka et a1 57/5889 UX FOREIGNPATENTS OR APPLICATIONS 489,538 12/1929 Germany 57/5891 825,776 12/1959Great Britain 57/5889 Primary ExaminerWerner H. SchroederAttorney-Robert E. Burns and Emmanuel J. Lobato [57] ABSTRACT A methodfor producing spun yarn in an open-end spinning system having a rotaryopen-ended spinning chamber comprises feeding a bundle of fibers to theopen-ended spinning chamber, rotating the openended spinning chamber ata peripheral surface speed V to successively accumulate superimposedlayers of fibers upon the peripheral surface of the spinning chamber,withdrawing the accumulated fiber layers 2 Claims, 12 Drawing FiguresPAIENIEuucTaoms 13,768,246 SHEET 3 OF 4 MOMENT CURVATURE- RESIDUALBREAKING STRENGTH in 'o s o I60 I50 "260' UNTWISTING RATE in%-PATENTEDnmsn ms 3,768,246

SHEET 4 OF 4 F/G. m F1678 FIG. 70

SPUN YARN AND ITS DOUBLED YARN AND THE PROCESS FOR MANUFACTURING THESAME The present invention, is a divisional application of the U.S. Pat.application Ser. No. 691,056 filed on Dec.

15, now U.S. Pat. No. 3,501,907 by the same applicant of thepresentinvention, and relates to a method for manufacturing an improvedblended yarn having better doubling effect.

ln case of fiber blending in the conventional spinning system, a largerblending number'was required in order to obtain a blended yarn of auniformly mixed composition. Such enlargement of the blending numberusually entailed multiple staged fiber doubling operations resulting inan unfavourable increase in the production cost of the blended yarnobtained. 7

Such necessity for multiple staged fiberdoubling operations seemed to bemitigated to an appreciable extent by the employment of the recentlydeveloped open-end spinning system. However, the actual utilizationofthe conventional open-end spinning system in the fiber blending hasproved the fact that there still remains a difficulty in the adjustmentof the mechanical conditions in the system corresponding to the requireddegree of the doubling effect. In the conventional open-end spinningsystem, only a negative pressure within the rotor due to a high speedrotation of the rotor was utilized for sucking the material fibers intothe system from the given supply source. Thus, the peripheral speed ofthe rotor, which is a function of the rotating speed of the rotor andthe effective internal diameter of the rotor, should have been primarilydetermined in a close relation with the required negative pressure andthere was no room for the adjustment thereof, from the view point of theresulting blending effect.

Generally, it is well-known that twisting in the spinning operation isan inevitable operation for forming yarn made from a fleece comprising aplurality of fibers which are continuously gathered and aligned alongtheir lengthwise direction to bestow the strength of the yarn. Thetwisting of yarn by the ring spinning frame, flyer spinning frame, arealso well-known arts. These conventional twisting methods twist the yarnin the same way, that is, one end of the bundle of fibers if fixed whilethe other end of the bundle of fibers is turned continuously by therotation of the package of twisted yarn.

Generally, if the fibers of the fiber strand before twisting can bemaintained in the twisting operation and the relative positions of eachfiber in the fiber strand do not change even after the twistingoperation, the fibers are occupied in the respective layer of theconfiguration of yarn. Consequently, the projection length of the fibertoward the axis of the yarn varies in accordance with the layer whereinthe fiber is occupied, in other words, the projection length of thefiber disposed in the outer layer of the yarn is shorter than that ofthe fiber disposed in the inner layer of the yarn. In fact, it cannot beconsidered that the fibers are stretched to form the above-mentionedconfiguration of yarn while the twisting operation is being performed.

of yarn, or vice versa. The above-mentioned phenomenon is generallycalled migration" in the field of textile technology. A yarn having theconfiguration of migration has such defects as the stiffness of the yarnincreasing with the continuance of the twisting while the resilience ofthe yarn degrades with decrease of the twisting. Consequently, it isvery difficult to produce spun yarn having a soft feeling of touch andsufficient resiliency by the conventional twisting methods.

A principal object of the present invention is to provide an improvedblended yarn having an uniformly blended composition and an excellentbulkiness, and a method for producing the same.

Another object of the present invention is to obtain a fabric havingsuperior handling quality provided by the improved blended yarn of thepresent invention.

In conformity with the above-described objects of the invention, themethod of the present invention utilizes, basically, the art of open-endspinning, wherein a pneumatic flow ejection caused by compressed air onthe supplied fiber bundle is employed for the purpose of fiber suckingand liberating. The mentioned liberating force on the supplied fibersbecomes dependent upon the additional pneumatic force. So, it becomespossible to change the mentioned peripheral speed of the rotor from theview point of the blending effect with less regard to the sucking andliberating effect. Thus, the peripheral speed of the rotor can bechanged freely in relation with the taking-up speed of the blended yarnand the required self-doubling number. As a result of such an adjustmentof the mechanical condition of the rotor, the actual self-doublingeffect acquired on said blended yarn becomes larger than the doublingeffect obtained by a' conventional spinning system whose doubling numberis equal to that defined by the mentioned relation.

Further features and advantages of the invention will be apparent fromthe ensuing description with reference to the accompanying drawings;wherein FIG. 1 is a skeleton sketch of an embodiment of the spinningdevice used for carrying out the method of the invention,

FIG. 2 is an explanatory drawing of the twisting mechanism of thespinning device shown in FIG. 1,

FIG. 3 is an enlarged side view of an embodiment of the spun yarnproduced by the method of the invention,

FIG. 4A, 4B and 4C are explanatory drawings showing the shapes of thefibers in the conventional yarn and the yarns of the present invention,respectively,

FIG. 5 is an explanatory diagram showing the bending moment of a yarn,

FIG. 6 is a diagram showing a relation between the residual strength ofa yarn and the rate of back twist for the conventional spun yarn and theyarn of the present invention,

FIGS. 7A, 7B and 7C are several embodiments of the spinning device forproducing blended yarn having the fiber configuration shown in FIGS. 38and 3C,

FIG. 8 is an enlarged cross sectional view of the blended yarn producedby the spinning device shown in FIG. 7B,

Recently, blending of several kind of fibers has been developed formanufacturing a blended spun yarn. One remarkable example is a blendedyarn of acrylic fiber with another kind of fiber having of superiorbulkiness. The high-bulky acrylic blended yarn has a large market in thefield of knitted fabrics. The properties such as bulkiness of theblended yam mentioned above can be improved remarkably by applying theparticular configuration of yarn of the present invention.

Generally one of the features required in the blended yarn is uniformcondition of the blending fibers. In case of knitting yarn such as ahigh-bulky acrylic yarn, some desirable mechanical properties such assoft feeling of touch and sufficient resiliency of the blended yarn arealways required. As the spun yarn of the invention has a particularconfiguration without migration, the above-mentioned preferablemechanical properties can be acquired by the configuration of the yarnof the invention. Further, a very superior blending effect, which wasnot obtained by the conventional spinning method,

can be obtained by the self-doubling effect of the rotating rotor of thespinning device shown in FIG. 1.

To obtain soft feeling of touch and superior resiliency of a yarn, theyarn must have a novel configuration without migration. Such yarn can bemanufactured by the spinning device shown in FIG. 1. The twistingmechanism of the spinning device shown in FIG. 1 differs completely fromthat of the conventional twisting mechanism. That is, one end of thebundle of fibers is turned while the other end of the bundle of fibersreceives no restriction during the twisting operation. A detailedillustration of the above-mentioned twisting mechanism and its operationare as follows:

A bundle of fibers l is supplied successively from a draft devicecomprising a trumpet 2, a pair of back rollers 3, 3', a pair of middlerollers 4, 4', and a pair of front rollers 5, 5', and the suppliedbundle of fibers is sucked into a guide inlet of a supply device 8wherein the sucking force is caused by compressed air supplied from acompressed air supply source. Fibers 6 sucked into the supply device 8are individually separated from the composite bundle 1 by the air forcejust after leaving the nip point of the front rollers 5, 5', and are fedto a rotor in a liberated condition through the delivery pipe 9 of thesupply device 8 by the air stream feeding means. The outlet of thedelivery pipe 9 points toward the inside peripheral wall of the rotor 10as shown in FIG. 2. The rotor 10 is formed in a pot-like shape and issupported by a vertical cylindrical axis 13 rotatably supported by amachine frame 11 through a bearing 12 and is rotated at a high rotatingspeed by a driving belt 16. The fibers liberated from the bundle l areejected and deposited successively, adhering to the inside wall of therotor 10 caused by the centrifugal force and air stream, and rotated bythe rotor 10 at a high rotating speed. The liberated fibers thusdeposited upon the inside wall of the rotor 10 are collected forrebundling and twisting into a form of a complete spinning yarn l5 andtaken up by a pair of take-up rollers 19 disposed downstream of theoutlet of the cylindrical axis 13.

In the above-mentioned twisting mechanism, the liberated fibers l adhereto the inside wall of the rotor 10 by the centrifugal force and aresuccessively accumulated, whereby a self-doubling effect is imparted tothe rebundled fibers released from the inside wall of the rotor 10. Theexpression self-doubling effect" is explained as follows. Generally, inthe spinning operation, uneveness in the thickness of the products suchas a sliver or roving is decreased by so-called doubling of a pluralityof the products during the drafting operation. This effect is called adoubling effect. However, in the present case, only the liberated fiberssuccessively fed from the delivery pipe 9 are doubled by theiraccumulation upon the inside wall of the rotor 10 in the form ofmutually superimposed successive layers. In other words, the suppliedbundle of fibers l is liberated into numerous individual fibers anddoubled successively by the above-mentioned manner. Consequently,unevenness in the thickness of the supplied bundle of fibers 1 can bereduced remarkably. The abovementioned effect is hereinafter called aself-doubling effect. The fiber bundle released from the inside wall ofthe rotor 10 is positively turned at the position where the bundle offibers is released from the inside wall of the rotor 10 while each fiberof the fiber bundle does not receive restriction to change in therelative aligned position of fibers because the fiber bundle isaccumulated upon the inside wall of the rotor 10 by the centrifugalforce due to the high speed rotation of the rotor 10.

As mentioned above, the liberated fibers supplied from the pipe 9 to theinside wall of the rotor 10 are accumulated ina uniform condition ofalignment while being provided with a self-doubling effect. Now,supposing that the inside radius of the rotor is R in meter, number ofrevolution of the rotor is M rpm, the surface speed of the inside wallof the rotor 10 is V meter per min., releasing speed of the bundle offibers from the inside wall of the rotor 10 is W meter per min., anarbitrary point on the inside wall of the rotor is designated as pointP, and the bundle of fibers is released from the inside wall of therotor 10 at the position designated by point P at the time function I T,the releasing point on the inside wall of the rotor 10 travels along theinside wall of the rotor 10 at a speed of W meter per min. whilereleasing the bundle of fibers continuously from the inside wall of therotor 10, and the releasing point returns to the original point P at thetime t T 2'rrR/W min., that is, after a passage of 21rR/W min. While thereleasing point of the bundle of fibers travels as mentioned above, therotor 10 rotates M X 27rR/W V/W turns. As the liberated fibers arecontinuously blown to the inside wall of the rotor 10 while thereleasing point is traveling along the inside wall of the rotor, it canbe considered that the liberated fibers are blown V/ W times upon theposition designated by the takingoff point P until the releasing pointreturns to the original point P. Now, supposing that the average numberof fibers contained in the cross-section of the supplied roving is N,that the draft ratio of the draft element is D and that the surfacespeed of the front roller is U meter per min., the supplied roving isdrafted at V/U times while passing through the draft zone formed betweenthe nip point of the rollers 5, 5' and the inside wall of the rotor 10.Consequently, the bundle of fibers, wherein the average number of fibersn in the crosssection is considered as NU/DV, adheres upon the insidewall of the rotor at every revolution of the rotor 10. Thus, the bundlesof fibers, wherein the average number of fibers in its cross-section isn, are doubled by V/ W. In other words, the drafted roving in theliberated condition is self-doubled by V/ W, that is, the produced spunyarn has a doubling number equal to V/W. The above-mentioned doublingoperation is performed at any position in the inside wall of the rotor.The fibers accumulated on the inside wall of the rotor 10 only maintaintheir relative positions along the thickness direction within the bundleof fibers chiefly by the centrifugal force. Further, the releasingpoints of the bundle of fibers from the inside wall of the rotor 10 arenot fixed at one releasing point P resulting in no disturbance of thementioned relative positions. Consequently, no migration takes placeduring the twisting operation in the above-mentioned embodiment of theinvention, and a spun yarn having uniform thickness due to theself-doubling effect of the rotor rotation can be manufactured.

When releasing the bundle of fibers continuously from the inside wall ofthe rotor 10, it is necessary to keep the force restricting the freeturning of the bundle of fibers at the-releasing point on the'insidewall of the rotor 10 at a suitable magnitude. The force restricting thefree turning of the bundle of fibers is mainly the frictional forcebetween the bundle of fibers and the inside wall of the rotor 10. Theabove-mentioned frictional force may be defined by the product ofcentrifugal force working on the bundle of fibers by the coefficient offriction between the bundle of fibers and the inside wall of the rotor10. According to our experimental tests, when the diameter of thelargest portion of the rotor 10 is 50 mm, the rotating speed of therotor 10 is 30,000 r.p.m., the preferable coefficient of frictionbetween the bundle of fibers and the inside wall of the rotor 10 is in arange from 0.2 to 0.7. The abovementioned coefficient of friction wasmeasured by the well-known Roder method at a linear speed of 50 metersper minute. The metallic inside wall of the rotor having a roughenedplated surface is suitable for obtaining the above-mentioned preferablecondition.

Someembodiments of the manufacturing method of the blended spun yarnaccording to the present invention are shown in FIGS. 7A, 7B and 7C.These manufacturing methods are characterized by the process comprisingliberating a plurality of bundles of fibers of different kinds in afluid stream, carrying the liberated fibers to the inside wall of arotor through a delivery pipe or pipes, accumulating the suppliedliberated fibers upon the inside wall of the rotor continuously bycentrifugal force and the air stream, releasing the accumulated bundleof blended fibers from the inside wall of the rotor while twisting,taking up the twisted bundle of blended fibers through an aperturedisposed to the central bottom of the rotor and onto a package. In theabove-mentioned explanation, the term different kinds of fibers meansfibers different in staple form" or fibers having different fineness orcut length, or different mechanical properties or different colors."

Referring to FIG. 7A, a single roving 31 of a blend of two differentfibers is supplied to the draft element, while in FIG. 73 two rovings 31and 3f of different fibers are supplied to the draft elementin a doubledcondition and the liberated different fibers in the double rovings arecarried to the inside surface of the rotating rotor 40 through a singledelivery pipe 39. On the other hand, in the embodiment shown in FIG. 7C,two rovings 31 and 31' of different fibers are supplied to therespective draft elements separately, and the respective liberatedfibers are supplied to the inside surface of the same rotor 40 throughthe respective delivery pipes 39 and 39 independently. By theabove-mentioned function of the rotor 40, the self-doubling effect canbe obtained in the three cases mentioned above. Consequently, a veryuniform blending effect can be obtained. That is, as already illustratedin the explanation of the function of the rotor shown in FIG. 2,supposing the average number of fibers contained in the respectiverovings are N and N, the bundle of fibers comprising a plurality offibers, whose number n or n in its cross-section is calculated as nNU/DV or n N'U/DV, are doubled and adhered upon the inside wall of theroller 40. The number of the above-mentioned doubling can be calculatedas V/W. Consequently, the bundle of fibers released from the inside wallof the rotor '40 contains two kind of fibers comprising a plurality offibers represented by the following equation (N N')/D U/W and a perfectblending condition similar to the doubling of V/ W bundles of fibers canbe expected. Further, by the twising of the abovementioned system, theblended yarn has novel configuration without migration. Consequently,the blended yarn having superior mechanical properties such as a softhand feeling, high bulkiness and strong resiliency can be obtained. Themechanisms of the spinning deas that shown in FIG. 1, in which thespinning material is supplied to the back rollers 35, 35' and drafted bythe draft zone comprising the back rollers 35 and 35', middle rollers 36and 36', apron 36" and front rollers 37 and 37. The drafted bundle offibers is sucked into the delivery pipe 39 or 39', and carried to therotating rotor 40 in a liberated condition by the air stream, and theaccumulated bundle of fibers is released from the inside wall of therotor 40 and advanced to the outside of the rotor through a bottomaperture formed through the central hollow shaft 40' of the rotor 40during the twisting operation and the manufactured blended yarn 44 istaken up onto a package.

The above-mentioned features of the yarn manufactured by the method ofthe invention will be more clearly understood from the followingexamples.

EXAMPLE I Fiber used 1.5 den. X 38 mm polyester staple fiber Total draftl8 Yarn count 26' (English system) Delivery speed of the front roller(U) meter/min Rotating speed of the rotor 32,000 r.p.m.

Peripheral speed of the inside wall of the rotor (V) 3,000 meter/minRadius of the rotor 50 mm Taking-up speed of the yarn (W) 50 meter/minCompressed air pressure 0.25 kg/cm Referring to FIG. 8, it was noticedthat the fibers contained in the yarn were blended in the cross-sectionof the yarn. I

It is one of the outstanding features of the invention that a blendedyarn having satisfactory blending of fibers can be easily manufacturedby the method of the invention in spite of the'very short-cut spinningsystem whose blending effect is superior to that in the conventionalspinning system whosedoubling number corresponds to V/W.

In the above illustration, some embodiments for blending two kind offibers are explained and the blending principle of the present inventionmay be applicable to the blending of more than two kinds of fibers.

Further, the blending principle of the present invention may be appliedto the so-called direct spinning system, wherein two kind of tows aresupplied to the draftcut device of the respective direct spinningequipments separately, next the bundles of fibers produced by thedraft-cut device are supplied to a pair of front rollers like thoseshown in FIGS. 7A to 7C separately or in a doubled condition, then fedto the twisting device in the same way as shown in FIGS. 7A to 7C.

A microscopic test on the spun yarn shown in FIG. 3 proved the lesserextent or absence of fiber migration in the configuration of the yarn.The twist configuration of the yarn shown in FIG. 3 is characterized bya plurality of outer-to-inner continuously, concentrically and spirallylayered twisted fibers. There is no definite boundary between the layersand the fibers in the inner layers are provided with a smaller number ofspiral coils and smaller coil diameters while fibers in the outer layersare provided with a larger number of spiral coils and larger coildiameters. Fibers of a particular layer are provided with lengthwiseuniform coil diameters.

Configuration models of the twisted fibers contained in the conventionalyarn and in yarns manufactured by the method of the invention areillustrated in FIGS. 4A, 4B and 4C, wherein fibers in the outer layersare designated with letters a, c and e while fibers in the inner layersare designated with letters b, d andf.

Provided that the number of fibers in the yarn crosssection are equaland respective yarns are subjected to bending deformations under thesame loading conditions, the bending deformation of the fibers in theouter layers is larger than that in the inner layers, that is, the outeris the layer, the larger is the contribution of fibers in the layer tothe stress of the yarn. On the other hand, it might be well understoodthat the smaller the coil pitch the larger the coil number and thelesser the resilience is to the bending deformation. In other words,fibers in the outer layer have a weaker resistance to bending whilefibers in the inner layer have a stronger resistance.

Consequently, it is clearly understood that the yarn having a twistconfiguration composed of fibers such as a and b shown in FIG. 4A has astronger resistance to the bending deformation than the yarn having atwist configuration composed of fibers such as c and d, e and f shown inFIGS. 48 and 4C, respectively. Concerning the torsional deformation, theyarn of the invention is easier to twist than the conventional yarn bythe same reason as mentioned above. Therefore, the yarn of the inventionshown in FIGS. 43 and 4C is softer than the conventional yarn shown inFIG. 4A.

In the yarn of the present invention, the interference of the fibers inthe inner layer to the fibers in the outer layer is very small. In otherwords, the fibers in the inner layer and the outer layer of the yarn canbe deformed independently from each other. Consequently, the frictionalresistance between the fibers in the inner layer and the outer layer canbe considered as being very small.

On' the other hand, it is well-known that the friction between theindividual fibers dominates the resiliency of the yarn in a small rangeof the deformation. Consequently, it can be considered that the yarn ofthe invention has superior resiliency.

EXAMPLE 2 A small amount of fibers dyed in black color was blended whenspinning a yarn of polyester staple fiber and the yarn manufactured onthe system shown in FIG. 1.

The rotation speed of the rotor 10 was 31,000 rpm. and theabove-mentioned coefficient of friction measured by the Rc'ider methodwas 0.46.

The yarn produced was mounted with a tricrosylphosphate liquid, then theyarn was observed with a microscope by inserting a sensitive filter (530my.) to a polarized light microscope with crossed-nicol. It was foundfrom this test that there was no migration.

EXAMPLE 3 A spun yarn of polypropylene was manufactured in the samespinning condition. The mechanical properties of the yarn are shown inTable 1 together with the mechanical properties of the conventional yarnmanufactured by the ring spinning system for the purpose of comparison.

TABLE I kind of yarn Yarn of the Conventional invention yarn Yarn countin English system 21 20.8 Number of twist tums/inch 16.3 16.0 Breakingstrength in g. 860 996 Breaking elongation in 20.6 21.5 Bendingstiffness CD 0.16 0.21 F 7.1 10.5 F/CD 44 5O I nitted cloth CD 0.18 0.24F 11.4 18.1 F/CD 63.5 75.4 Bulkiness in cm lg. 73 65 coefficient ofcompressibility 35.9 39.6

In the Table 1, the bending stiffness of the yarn and its knitted clothwere measured in the following manner.

The hysteresis curve of the bending stiffness of the test piece in asheet form with respect to the bending curvature of the test piece wasrecorded. One example of the above-mentioned hysteresis curve is shownin FIG. 5, wherein the average inclination of the curve between thepoints A and B is represented by CD. It is considered that the testpiece is easier to bend, if the value of CT) is larger.

Further, the distance between points A and B is represented by F whichis considered as a frictional force at the time of the bendingdeformation of the test piece in a sheet form. Then the value of F/C Dis calculated, and it is considered that the resilience of the testpiece in a sheet form is larger if the value of F/CD is smaller.

The above-mentioned method of estimation was confirmed by repeatedexperimental test. Further, the results obtained by the present methodexhibited the socalled functional feeling or handling quality of thetest piece of the cloth. Thirty pieces of yarn aligned in a parallelcondition with 20 mm width were prepared for the test. The test piecesof knitted cloth were cut in a width of 20 mm and the distance betweenthe grips was 4 mm. The mechanical properties of the yarn shown in theTable l prove the yarn of the present invention has superior resiliencyand soft feeling of touch.

ln Table l, the bulkiness of the test piece was measured with theconventional instrument for measuring thickness of the test piececontinuously under a changing load. The original thickness of the testpiece was measured under a load of 2 g/cm for calculating the specificvolume of the test piece. Results in Table I show the yarn of theinvention is bulkier than the conventional yarn.

As already explained, the yarn of the present invention has a novelinternal configuration wherein there is no migration and each fibercontained in the yarn is provided with a plurality of spiral coils withalmost uniform diameter with respect to the yarn axis. Consequently,when the yarn of the present invention is untwisted the yarn canmaintain its internal configuration while, in case of the conventionalyarn, the yarn loses its twisted configuration by untwisting and thenloses its strength, thereof. To make clear the difference of the effectof untwisting of the yarns of the present invention and the conventionalyarn, the relation between the residual strength of yarn and the rate ofback twist of both yarns are shown in FIG. 6, wherein the curve arepresents the case of the conventional yarn while the curve brepresents the case of the yarn of the present invention.

As is clearly shown in the diagram, the residual strength of the yarn atthe rate of back twist of 100 percent is still more than zero and theresidual strength of the yarn at the rate of back twist of 75 percent ismore than 30 percent of the original strength. As indicated by theexperimental test, it is impossible to impart to the spun yarn of theinvention'a no twist configuration. Consequently, it is clearlyunderstood that the spiral configuration of fibers in the outer layersand inner layers of the yarn is not the same. In the above-mentionedillustration, the residual strength of the yarn and the rate of the backtwist are defined as follows:

Residual strength Breaking strength of the back twisted yarn Originalbreaking strength of the yarn Number of turns for back twisting Originalnumber of twist What is claimed is:

1. A method for producing spun yarn on an open-end spinning machinehaving an open-ended spinning chamber comprising: providing a bundle offibers to be spun into yarn; transporting said bundle of fibers in anair stream to an inner peripheral surface portion of an open-endedspinning chamber while individually separating the fibers; rotating saidopen-ended spinning chamber at a peripheral surface speed V toaccumulate longitudinally successive, superimposed layers of separatedfibers upon the inner peripheral surface portion of said open-endedspinning chamber; longitudinally withdrawing the accumulated fiberlayers from the rotating open-ended spinning chamber in the form of spunyarn at a withdrawing speed W to effect selfdoubling of the spun yarn ata doubling number V/ W; and selectively varying the peripheral surfacespeed V and the withdrawing speed W to provide the spun yarn with apredetermined doubling number V/W during only a single passage throughthe open-end spinning machine.

2. A method according to claim 1; wherein said pro viding stepcomprising providing a bundle of fibers composed of at least twodifferent kinds of fibers.

1. A method for producing spun yarn on an open-end spinning machinehaving an open-ended spinning chamber comprising: providing a bundle offibers to be spun into yarn; transporting said bundle of fibers in anair stream to an inner peripheral surface portion of an open-endedspinning chamber while individually separating the fibers; rotating saidopen-ended spinning chamber at a peripheral surface speed V toaccumulate longItudinally successive, superimposed layers of separatedfibers upon the inner peripheral surface portion of said openendedspinning chamber; longitudinally withdrawing the accumulated fiberlayers from the rotating open-ended spinning chamber in the form of spunyarn at a withdrawing speed W to effect self-doubling of the spun yarnat a doubling number V/W; and selectively varying the peripheral surfacespeed V and the withdrawing speed W to provide the spun yarn with apredetermined doubling number V/W during only a single passage throughthe open-end spinning machine.
 2. A method according to claim 1; whereinsaid providing step comprising providing a bundle of fibers composed ofat least two different kinds of fibers.